Steve Bertrand

NAME

RPi::ADC::MCP3008 - Interface to the MCP3008 analog to digital converter (ADC) on Raspberry Pi

DESCRIPTION

Provides access to the 10-bit, 8 channel MCP3008 analog to digital converter over the SPI bus, on the dedicated hardware SPI channel pins CE0 (0) or CE1 (1), or use any GPIO pin for the CS pin and bit-bang the SPI to keep free the hardware SPI CS pins.

Requires wiringPi to be installed, as well as access to the C pthread library.

This library should work equally well with the MCP3002 and MCP3004, although I have not tested them.

You can review the MCP3008 datasheet or the breadboard layout.

SYNOPSIS

    use RPi::ADC::MCP3008;

    # 0 or 1 for channel use the onboard hardware CE0
    # or CE1 SPI CS pins. Set to any GPIO pin other than
    # 0 or 1 to use that GPIO pin as your CS instead

    my $spi_channel = 0; # built-in CE0
    # $spi_channel = 21; # use GPIO pin 21 as CS instead

    my $adc = RPi::ADC::MCP3008->new($spi_channel);

    my $adc_channel = 0;

    my $r = $adc->raw($adc_channel);

    ...

METHODS

new

Instantiates and returns a new RPi::ADC::MCP3008 object after initializing the SPI bus.

Parameters:

    $channel

Mandatory: Integer, the SPI bus channel to communicate over. 0 for /dev/spidev0.0 or 1 for /dev/spidev0.1. Alternatively, send in any GPIO pin number (above 1), and we'll use that GPIO pin as the CS pin instead, freeing up the two hardware SPI channel pins. We do this by bit-banging the SPI bus in this case.

raw

Fetch the raw data from the chosen channel as an integer between 0 - 1023

Parameters:

    $adc_channel

Mandatory: Integer, the ADC input channel to read. 0 - 7 for single-ended (channels CH0-CH7), and between 8 - 15 for differential. See "CHANNEL SELECT" for full details on all the various options.

percent

Fetch the input level as a double floating point number percentage.

Parameters:

    $adc_channel

Mandatory: Integer, the ADC input channel to read. 0 - 7 for single-ended (channels CH0-CH7), and between 8 - 15 for differential. See "CHANNEL SELECT" for full details on all the various options.

TECHNICAL DATA

CHANNEL SELECT

The MCP3008 allows both single-ended and differential modes of operation. Single-ended means read the difference of voltage between a single pin and Gnd. Double-ended means the difference in voltage between two input pins. Here's a table explaining the various options, and their parameter value. The left-most bit represents the mode. 1 for single-ended, and 0 for differential:

    Param   Bits    Dec     Hex     ADC Channel
    -------------------------------------------

    0       1000    8       0x08    CH0
    1       1001    9       0x09    CH1
    2       1010    10      0x0A    CH2
    3       1011    11      0x0B    CH3
    4       1100    12      0x0C    CH4
    5       1101    13      0x0D    CH5
    6       1110    14      0x0E    CH6
    7       1111    15      0X0F    CH7

    8       0000    0       0x00    CH0+ | CH1-
    9       0001    1       0x01    CH0- | CH1+
    10      0010    2       0x02    CH2+ | CH3-
    11      0011    3       0x03    CH2- | CH3+
    12      0100    4       0x04    CH4+ | CH5-
    13      0101    5       0x05    CH4- | CH5+
    14      0110    6       0x06    CH6+ | CH7-
    15      0111    7       0x07    CH6- | CH7+

AUTHOR

Steve Bertrand, <steveb at cpan.org>

LICENSE AND COPYRIGHT

Copyright 2017 Steve Bertrand.

This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License.

See http://dev.perl.org/licenses/ for more information.